rtc: mc13xxx: fix a double-unlock issue

rtc: mc13xxx: fix a double-unlock issue

In function mc13xxx_rtc_probe, the mc13xxx_unlock() is called
before rtc_register_device(). But in the error path of
rtc_register_device(), the mc13xxx_unlock() is called again,
which causes a double-unlock problem. Thus add a call of the
function “mc13xxx_lock” in an if branch for the completion
of the exception handling.

Fixes: e4ae7023e182a ("rtc: mc13xxx: set range")
Signed-off-by: Qiushi Wu <wu000273@umn.edu>
Link: https://lore.kernel.org/r/20200503182235.1652-1-wu000273@umn.edu
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>